The invention relates to an optical fiber connector wherein the optical fiber within the connector is surrounded by a ferrule. Such a connector is used for detachably joining ends of optical fibers such that light emerging from the end of one fiber is coupled into an opposite fiber with as much efficiency as possible. The invention also relates to a method for manufacturing such a connector.
Due to refractive index steps at the fiber ends there may be unwanted light reflections in the coupling region of the fibers. Light leaving a fiber may for example be reflected at such an interface back into the fiber and cause various disturbances in the fiber optic system of which the fiber is a part. This return radiation can be especially troublesome in systems wherein measuring or data signals are transmitted along the fibers. It is therefore desirable to have fiber optical connectors wherein such returning light does not occur, i.e., to have connectors with high return loss. Particularly, modern fiber optical communication systems require fiber optic connectors with high return loss.
As a result of the efforts to achieve high return loss, three different types of fiber optical connectors have been developed:
According to a first approach, the endfaces of the two connectors (i.e., the fiber and ferrule endfaces) are arranged perpendicularly with respect to the longitudinal axis of the fiber and the end faces of the two opposite fibers are in contact with each other. According to a second type of connectors, the opposite fiber end faces are spaced apart and the gap between the end faces is filled with index matching fluid to avoid glass-to-air transitions which would cause reflections. In a third approach, the endfaces of both connectors are inclined under a certain angle with respect to the connector axis and the two connectors are joined together such that the fiber end faces are not in contact with each other. Although reflections from the glass-to-air transitions occur, they are reflected back into the glass at an angle which is greater than the acceptance angle of the fiber core. Therefore, reflected light is stripped from the fiber and does not influence the performance of the fiber link.
Among the above mentioned three alternatives, the third typically has good performance characteristics regarding return loss. Such connectors, however, are difficult to manufacture and lack compatibility with the very common fiber connection systems with 2.5 mm ferrule diameter. In particular, since the width of the air gap between the two fiber end faces has to be precisely maintained, the connector has to be furnished with additional mechanical parts which permit the very exact adjustment of the required distance between the opposite fibers. The known connector thus becomes mechanically complex with great demands on the manufacturing tolerances of the used parts.